Discoveries in Research

Commonly held view in geophysical community that water is carried deep into Earth’s mantle is false, says UC Riverside’s Harry Green

RIVERSIDE, Calif. – A popular view among geophysicists is that large amounts of water are carried from the oceans to the deep mantle in “subduction zones,” which are boundaries where the Earth’s crustal plates converge, with one plate riding over the other.

But now geophysicists led by the University of California, Riverside’s Harry Green, a distinguished professor of geology and geophysics, present results that contradict this view. They compare seismic and experimental evidence to argue that subducting slabs do not carry water deeper than about 400 kilometers.

“The importance of this work is two-fold,” Green said. “Firstly, if deep slabs are dry, it implies that they are strong, a major current question in geophysics that has implications for plate tectonic models. Secondly, even small amounts of water greatly reduce the viscosity of rocks; if water is not cycled deep into Earth, it means that mantle convection has not been as vigorous over time as it would have been with significant water.”

Fossils Represent Large-scale Life Forms

A team of paleontologists led by Mary Droser, chair of the Department of Earth Sciences, spent the month of July in the South Australian outback excavating fossils from the Ediacaran period of geologic history (630–542 million years old). The fossils unearthed from the outback’s red soils represent the first evolution of large-scale life forms, and are one of our best windows into understanding the origins of life on Earth. Accompanied by a paleontologist from the South Australian Museum, Droser and one of her graduate students, Lucas Joel, worked on analyzing Ediacaran trace fossils (a trace fossil is like a footprint that offers clues to behavior).

“While there were no dinosaurs walking around during the Ediacaran, the trace fossils from this time period are just as exciting,” Joel said. “The traces we’re looking at represent the very first appearance of mobile, bilaterian animals. Bilaterian animals include humans, insects, fish … anything with bilateral symmetry.”

He explained that mostly all Ediacaran animals vanish from the fossil record around 542 million years ago. This apparent mass extinction is important for understanding current ecosystem collapses, and will be a focus of future research in Droser’s lab.

Oxygen Oases Sites Set Stage for Life

Geochemists Timothy Lyons and his graduate student Christopher Reinhard have contributed to a study that reports that oxygen oases in the surface ocean near the continents were sites of significant oxygen production at least 100 million years before the gas began to rise sharply in the Earth’s atmosphere 2.4 billion years ago, which then set the stage for animal life to follow.

They worked with scientists from Arizona State University (ASU), who led the study.

In a paper published Aug. 22 in Nature Geoscience online the research team reports that cyanobacteria were responsible for the production of oxygen via photosynthesis along the ocean margins.

For this research, the team focused on well-preserved rocks drilled in South Africa that are more than 2.5 billion years old. While the ASU researchers focused on rhenium and molybdenum abundances to find evidence of dissolved oxygen on the seafloor, Reinhard and Lyons studied iron chemistry in the same shales.

Their data supports the presence of oxygen in the surface ocean but also reveal oxygen-free conditions in the deep waters with abundant dissolved iron and hydrogen sulfide.

Grants from the National Science Foundation and NASA supported the UCR contribution to the study. Drilling costs were financed by the Agouron Institute.

New Picture of Ancient Ocean Chemistry Argues for Chemically Layered Water

RIVERSIDE, Calif. – A research team led by biogeochemists at the University of California, Riverside has developed a detailed and dynamic three-dimensional model of Earth’s early ocean chemistry that can significantly advance our understanding of how early animal life evolved on the planet.

Working on rock samples from the Doushantuo Formation of South China, one of the oldest fossil beds and long viewed by paleontologists to be a window to early animal evolution, the research team is the first to show that Earth’s early ocean chemistry during a large portion of the Ediacaran Period (635-551 million years ago) was far more complex than previously imagined.

Their work is the first comprehensive geochemical study of the Doushantuo Formation to investigate the structure of the ocean going from shallow to deep water environments. It is also one of the most comprehensive studies for any Precambrian interval. (The Precambrian refers to a stretch of time spanning from the inception of the Earth approximately 4.5 billion years ago to about 540 million years ago. It was in the Precambrian when the first single-celled microbes evolved 3.5 billion years ago or earlier, followed by the first multicellular animals much later, around 700 million years ago.)

The researchers’ model for the ancient ocean argues for a stratified marine basin, one with a chemically layered water column. While the surface ocean was oxygen-rich, the deep ocean was ferruginous – oxygen-deprived and iron-dominated. Further, sandwiched in this deep ocean was a dynamic wedge of sulfidic water, highly toxic to animal life, that impinged against the continental shelf.

Dominated by dissolved hydrogen sulfide, the sulfidic wedge was in a state of flux, varying in size and capable of encroaching on previously oxygenated areas of the continental shelf — killing all animal life there. The overall picture is a marine basin with co-existing oxygen-rich, sulfidic and ferruginous water layers.

Laptops could be key to an earthquake early-warning system

Seismologists envision a 'Quake Catchers' network of volunteers using their computers to precisely map tremors.

By Cara Mia DiMassa

If Elizabeth Cochran allowed herself to dream, the future would look something like this:

Every personal computer would double as a seismic monitor. That MacBook at the coffee house, the one used by the guy pounding out a screenplay? Working to detect ground tremors while its user sips a latte. The aging PC gathering dust in the guest room? Ready to catch the next quake.

If Cochran, an earth scientist at UC Riverside, has her way, every time the ground beneath us shakes, those machines would capture its movement and feed the information to a central computer system, creating a rich -- and inexpensive -- portrait of how and where an earthquake is felt. Such a network could dramatically boost our understanding of earthquakes -- and bring researchers a step closer to an earthquake early-warning system that could give emergency officials vital seconds of preparation as a catastrophic temblor moved through the region.

By harnessing the power of accelerometers -- tiny devices that detect movement, allowing iPhones to flip from vertical to horizontal and Wii devices to function as tennis rackets -- Cochran and her colleagues at Riverside and at Stanford University have begun to build a system that links ordinary computers into a seismic network.

Ideally, Cochran said, "we would have seismometers in every building, or at least on every block. And in tall buildings, we'd have multiple sensors [on different floors]. That way, we would be able to actually get much higher detail, images of how the ground shakes during an earthquake."